The invention is directed to a method for producing a winding protection for tape-wound cores with a polymer, particularly to a new hardening and enveloping process for optimally thin-walled insulation and simultaneous hardening of magnetic tape-wound cores.
Magnetic cores for electrical components are implemented as tape-wound cores, particularly as toroidal tape-wound cores, in many instances. These toroidal tape-wound cores usually have a cylindrical circumference and an inside opening in an axial direction. Such toroidal tape-wound cores are wound with one or more windings for manufacturing inductances and transformers. These windings are composed of insulated electrical wires or conductors such as, for example, an enameled copper wire. The winding must thereby be protected against damage by the edges of the magnetic core during winding.
Since toroidal tape-wound cores, which are wound of thin, cut tapes, exhibit extremely sharp edges, an edge protection is necessary. Due to the brittleness of the tapes, an edge protection is also needed for the inner and outer tape plies for toroidal tape-wound cores, that are composed of amorphous or nano-crystalline alloys, to protect them against the forces occurring during winding. In addition, the edge protection must be electrically insulating.
A further demand is the stabilization or, respectively, hardening of the tape-wound core, which represents an extremely unstable formed body because of its structure. This is less true of the inside or outside diameter of the toroidal tape-wound core, since these dimensions are fixed well by point welds at the inner and outer tapes to one another. What is particularly critical here is the core height, since this easily yields a displacement in the axial direction, dependent on various parameters such as, for example, winding tension, tape geometry, surface nature of the tapes, tape width, etc. Extremely different measures are known for preventing this change of the core geometry.
Dribbling and/or saturating the cores with a polymer is notoriously known. The hardening is obtained, for example, by emitting solvent or by a reaction of two components. What is thereby disadvantageous, however, is that a precise setting of the layer thickness is not possible with this method.
JP 7 211 530 A discloses a toroidal tape-wound core of a non-crystalline alloy coated with a polymer layer.
U.S. Pat No. 3,342,754 discloses details of a coating method with which a polymer layer can be applied to a surface. The method disclosed by U.S. Pat. No. 3,342,754 can be implemented under laboratory conditions but is not suited for use in mass production.
A number of methods are known for the “outer” protection of tape-wound cores. EP 0 677 856 A1 and EP 0 226 793 A1 disclose plastic housings that are adapted to the outer shape of the core, whereby an inner hardening can be foregone due to the intrinsically stable structure. German Utility Model 7726882 discloses various envelopes for toroidal cores of coils that are essentially intended to prevent the lacquer of the wire, which is applied onto the core, from being damaged by sharp edges of the core. This armoring with insulating foils, however, is work-intensive since, for example, given a tape-wound core, the foil must always be pulled through the middle of the core when armoring.
EP 0 621 612 A1 discloses the employment of a shrink hose shrunken on in an axial direction of the core that leads to a thin-walled fixing and to a protection of the inside and outside edges given a simultaneous stabilization of the core.
EP 0 351 861 A1 discloses the extrusion-coating of a toroidal tape-wound core with plastic in a tool. In addition to the edge protection and the core solidification, mounting and insulating parts can thus also be simultaneously manufactured.
However, there is the inherent disadvantage in all known methods that, on the one hand, they are extremely work-intensive and therefore not suited for mass production and, on the other hand, an exact and, in particular, extremely thin, constant layer cannot be set with them. Specifically given small cores, the traditional methods have the disadvantage that the ratio between the external volume (growth volume) and the magnetically used volume (net volume) becomes unbeneficial due to the necessary wall thicknesses of the envelope and the necessary joining tolerances when inserting the core. The magnetic use factor (gross volume/net volume) thereby increasingly diminishes and becomes considerably removed from the theoretical ideal value of 1.
The known methods wherein work is carried out with a polymer (saturating, dribbling, eddy sintering, etc.) lead to considerable modifications of the magnetic properties. This results from the volume change of the polymers during or after the polymerization step. The shrinkage forces which occur, as well as compressive and tensile stresses, effect the modification of the tape-wound core properties because of the magneto-striction of the soft-magnetic tapes.